In recent, bio-sensors such as DNA chip and protein chip use a label type fluorescence method to measure biomolecules in which the biomolecules are measured through fluorescence material, labeling. However, such label type method causes structural and functional changes of the biomolecules during the labeling process. Since the florescence method depends on optical signals to obtain data, it is difficult to apply semiconductor electronics technology to the bio-sensor. Further, there is problem in that the size of an optical measuring device is large to be portable or to embed in other systems.
Thus, a field effect transistor (FET) type bio-sensor capable of utilizing merits of a non-label type method and of combining micro-electronics and nano-technology is more excellent than currently widely used bio-sensors and sensors in above-mentioned technical view.
The above-mentioned conventional silicon semiconductor-based FET bio-sensor is advantageous in terms of utilizing a well-developed silicon process, but has a poor bonding characteristic between silicon and biomolecules. In order to overcome these problems, in the conventional art, to utilize the excellent bond characteristics of gold-sulfur (Au—S), a method of bonding thiol-groups (—SH) to biomolecules and then bonding the bonded product to gold thin film on a surface of the silicon is used.
However, the bonding of Au—S also has the following disadvantages. First, since Au is a typical contamination material to be avoided in a manufacturing line of semiconductors, it is difficult to utilize conventional manufacturing lines of semiconductor devices. Therefore, it is difficult to enter the market. Secondly, in a case of bonding the thiol-group to proximal ends of biomolecules, there is concern about deformation and loss of function of sensitive molecules such as protein.
Finally, the conventional bonding of Au—S has poor stability and a short life-span because it is easily affected by oxidation. These problems result in a relatively short shelf-life and restrictions for storage and transportation. Recently, a new bio-sensor technology using diamond thin film is on the rise. This technology has superior stability and shelf-life compared to that using the conventional Au—S bond because diamond and the biomolecules form carbon (C)-carbon (C) covalent bonds. Since the conventional diamond-based bio-sensor employs poly-crystalline diamond thin film as a conductive channel, defects such as grain boundaries contained in poly-crystalline diamond remarkably decrease mobility of carriers in comparison to conventional silicon semiconductor devices so that the conventional diamond-based bio-sensor does not have a performance superior to a Si-based bio-FET sensor using gold that has been researched. Such low mobility of carriers is a fatal drawback in forming a peripheral electronic circuit of a sensor to be coupled with micro-electronics. Moreover, there is a solution gate FET (SG-FET) bio-sensor using a diamond surface as a channel, however, since the SG-FET bio-sensor depends on only surface conduction of the diamond thin film, the adjustment of a channel by controlling a gate voltage is not possible, thus sensitivity of a sensor for biomolecules is not good. Moreover, the SG-FET mainly uses a way of measuring a change of pH due to reaction between biomolecules and enzymes to indirectly quantify biomolecules rather than directly detecting the biomolecules. Thus, there is a high risk of noise being mixed with a measured signal and a high possibility of malfunction of the sensor. Thus, there is required a new bio-sensor configuration capable of utilizing both of excellent bonding stability between biomolecules and diamond, and excellent channel characteristics of the silicon FET.